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  • hilborn mechanical fuel injection?

    hey, ya i was wondering if anyone could help explain to me the wokings of a hilborn mechanical fuel injection system. I know they use a distrbution block, but how does it actually distribute the proper fuel flow? And i was wondering if the whole set up is even streetable, because on the hilborn website it says thet it is "only good for high speed use" and not at all streetable, but then ive seen pics of some street driven gassers with hilborn stacks. So whats the deal?

  • #2
    Re: hilborn mechanical fuel injection?

    Not familiar with Hilborn MFI but in general, MFI systems use a barrel valve to control the amount of fuel and keep it in proportion to throttle position. Since mech FI doesn't have all the sensor inputs that EFI has it doesn't adapt to engine load, operating temp, weather, etc. like electronic fuel injection. That is why it is so good for racing but driveability is poor.

    Have seen some neat looking Hilborn setups that were converted to a hidden EFI. Now that would be cool.

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    • #3
      Re: hilborn mechanical fuel injection?

      isnt that system similar to what chevy diesels used in the 80's the fuel goes through a timing driven "distibution" pump to each cylinder, but had a block driven fuel pump.

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      • #4
        Re: hilborn mechanical fuel injection?

        Go to the man who makes Žem.

        http://www.hilborninjection.com/index.asp

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        • #5
          Re: hilborn mechanical fuel injection?

          The alchohol motor in the sprint car I've been helping with runs a Hilborn. The injector tubes act as jets.

          You can drive anything on the street if you want to bad enough. Hilborns will be fat as a pig on the street. Keep a couple extra sets of plugs in the glove box.
          The official Bangshift garage door guru. Just about anything can be built using garage door parts, trust me.

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          • #6
            Re: hilborn mechanical fuel injection?

            Originally posted by dagenesta
            The alchohol motor in the sprint car I've been helping with runs a Hilborn. The injector tubes act as jets.

            You can drive anything on the street if you want to bad enough. Hilborns will be fat as a pig on the street. Keep a couple extra sets of plugs in the glove box.
            true
            i did it ti is fun to a point lol
            more headachs then it was worth putting it on our race car
            basicly think of a gardon hose
            the engine is running turning the fuel pump and fuel is sent to the barral valve etc... if the enging is turning fuel if flowing

            chevk out this sight ton of great info more then i could type

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            • #7
              Re: hilborn mechanical fuel injection?

              you say the injectors are basically jets, so fuel is just brought out as air goes by? Or is it just a constant flow of fuel??

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              • #8
                Re: hilborn mechanical fuel injection?

                Its constant flow of fuel. The pump is a fixed displacement unit that directly translates engine rpm into fuel volume. The barrel valve controls how much fuel goes back into the return line the rest gets sprayed into the tubes via nozzles that control the rate at which it flows per specific pressure. I believe there is a jet in the system but its located in the fuel barrel valve and used to control the fuel flow to the distrobution system to the nozzles.
                Central TEXAS Sleeper
                USAF Physicist

                ROA# 9790

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                • #9
                  Re: hilborn mechanical fuel injection?

                  yep there is a jet the "pill"
                  is is before the nozles and anfter the pump {simple way to put it} and it is in the fuel line
                  they are tuchy too as to weather etc...
                  but man the response out of this world

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                  • #10
                    Re: hilborn mechanical fuel injection?

                    I'm trying to figure out why the crewchief for the team I help out changes injector tubes. They aren't the actual
                    "jet(s)"; must be some type of tuning tool.
                    The official Bangshift garage door guru. Just about anything can be built using garage door parts, trust me.

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                    • #11
                      Re: hilborn mechanical fuel injection?

                      probably trying to balance the tubes out cylinder to cylinder. They aren't all identical and you can play to the needs of the cylinder by matching a certain tube to it to try to run all of them at 99% vs a compromise and have them scattered.
                      Central TEXAS Sleeper
                      USAF Physicist

                      ROA# 9790

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                      • #12
                        Re: hilborn mechanical fuel injection?

                        Basically, (very basically);
                        You have the fuel pump (mechanical, usually belt driven), barrel valve, distribution block and nozzles in each throttle body.

                        The fuel pump moves a given amount of fuel per revolution, hence, the higher the engine RPM, the more fuel is pumped. Fuel flows up to the barrel valve, which functions as a tap and is mechanically connected to the throttle butterflies; more throttle opens the tap further, letting more fuel through the barrel valve and into the distribution block, and eventually out the nozzles in each throttle body.
                        Therefore fuel is metered via throttle position (more throttle opens the barrel valve further, lets more fuel through) and engine RPM (more RPM means the pump is moving more fuel).

                        There are then several 'bypasses' which allow some tuning. Main bypass is the main tuning tool, it runs from the pump back to the tank, returning fuel before it even reaches the barrel valve. It has a 'pill' or 'jet' in the line. . the bigger the main bypass pill, the more fuel returns to the tank and the leaner the mixture across the board. There is also a secondary bypass, this comes into effect at part throttle but has no effect at WOT. This is adjustable by both the size of the 'pill', and the fuel pressure at which it opens. Higher pressure setting means it works at a higher RPM (remembering fuel pressure is linked to RPM via the mechanical fuel pump), and the pill size determines how much fuel returns to the tank when it opens. Bigger pill, more fuel returns and the leaner it will make the mixture above the RPM the pressure setting has it operate.
                        There is also usually a high speed bypass, which works at WOT high RPM situations. Because an engine's fuel demand is not linear with RPM (efficiency increases at higher RPM, requires relatively less fuel), a linear rise in fuel would make the engine run fat at WOT high RPM, hence there is a high speed bypass. This works the same as secondary bypass, you set the pressure at which it works, and the pill for the amount of fuel it returns.
                        On more complex fuel systems, there are timed or manually operated bypasses that can be controlled by air or electric solenoids, to tailor the fuel delivery for certain situations, ie different gears, different conditions, etc etc. They can either be operated by the driver or setup to work on a gear shift or timer etc.

                        You can see, then, that because there is nothing in the metering system based on engine 'load', slow street driving will result in a mixture that is very fat and as has been said, you'll soot plugs like nobody's business.

                        You CAN get it to work on the street, in fact there is a car I wrote about in a magazine over here in Australia that not only sees regular street miles with a mechanical injected small block, but it has in fact been converted to use gasoline, not alcohol. It took a lot of hours on the fuel flow bench and the dyno, and someone very good at tuning mechanical injection, but it can be done.

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                        • #13
                          Re: hilborn mechanical fuel injection?

                          Thanks for the good informative post.

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                          • #14
                            Re: hilborn mechanical fuel injection?

                            WOw, I can imagine having that with 8 injectors spraying Nitrous.

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                            • #15
                              Re: hilborn mechanical fuel injection?

                              Originally posted by Fordplay0621
                              WOw, I can imagine having that with 8 injectors spraying Nitrous.
                              The car I wrote the story on did actually have a direct port nitrous system as well. . using fogger nozzles like an EFI nitrous system uses. It's one wild bit of gear.

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